The Moral Argument for God's existence can be stated simply:
Premise 1: If God does not exist, objective moral values and duties do not exist. Premise 2: Objective moral values and duties do exist. Conclusion: Therefore, God exists.
Premise 1 is grounded in the observation that in a purely materialistic universe there is no foundation for objective moral values. On atheism, human beings are simply advanced primates whose moral intuitions are the product of evolutionary pressures.
As Dostoevsky's Ivan Karamazov famously put it: 'If there is no God, everything is permitted.' Philosopher Michael Ruse, an atheist, has argued that morality is 'just an aid to survival and reproduction, and any deeper meaning is illusory.'
Premise 2 appeals to our deep moral intuitions. Virtually all human beings recognize that torturing children for fun, genocide, and rape are objectively wrong — not merely socially disapproved, but genuinely evil regardless of what any culture says. The Holocaust was wrong even though the Nazis sincerely believed otherwise.
If objective moral values exist, they require a foundation that transcends human opinion, cultural convention, and evolutionary programming. The most plausible foundation is a transcendent moral lawgiver — a being whose nature defines goodness itself.
C.S. Lewis developed this argument extensively in Mere Christianity, beginning with the observation that all human beings appeal to a moral standard they expect others to recognize.